Add TypeScript tooling for JavaScript type-checking

[aduth]

Why: To improve confidence in our code. The error fixed in #4040 would have never happened if these changes had been in place.

Applies only to new code in app/javascripts/app/document-capture (the React-based document capture flow).

See also: #4040

This removes prop-types and disables the associated ESLint configuration.

From #4040:

Benefits:

1. Can be used to provide type checking to surface these sorts of errors

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2. Can be used to provide type checking and props detailed information from rendering parent components

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3. Takes advantage of existing mechanisms for documenting functions using JSDoc
4. Affords opportunity to describe the purpose of the prop type in the detail of the custom @typedef
5. Provides an excuse timely and relevant space to describe the purpose of the component
6. Allows prop validation errors to be checked at build time, rather than at run time (if enabled in build step, see "Downsides")
7. Ships less code, since propTypes are only relevant for development, but are still shipped to production (unless steps are taken to strip them from production builds)
8. Removes a dependency (prop-types)
9. Allows prop defaults to be assigned using language-native defaulting syntax

[zachmargolis]

LGTM